As best known by owners of small animal pets, and particularly cats, the waste materials of these animals and especially the urine produce foul odors when permitted to stand for any appreciable amount of time. The approach which has generally been taken is to attempt to train or encourage the pet to excrete in one, most unobjectionable place within a dwelling or household. This has been successful to some extent by providing boxes or shallow containers filled with commercially available litter materials which tend to absorb the urine and to that extent assist in controlling the odors. Clearly, this approach is not fully effective and the problem may still be acute in small confined apartments where the litter box must of necessity be located in areas shared most frequently with pet's owners.
It may be possible, in some instances, to train the pet to leave the premises or dwelling prior to excretion. For this and other purposes there is known in the prior art various devices which permit an animal to freely come into and go out from a house. For example. an animal hatch is disclosed in U.S. Pat. No. 3,091,221; a windowgate assembly in U.S. Pat. No. 3,499,246; and a pet door apparatus in U.S. Pat. No. 3,690,299. However, it should be clear that these and other like devices are only useful when they can be located at or near ground level. Thus, they cannot be used in high rise apartments where the windows are substantially above ground level unless a balcony or the like exists. An additional problem which exists with these devices under discussion is that they do not confine the animal once they leave the house and this may expose the pet to danger and injury as well may permit the animal to escape or otherwise be lost. Additionally, an examination of the above patents reveals that the devices therein disclosed are typically mounted in or connected to the house or premises. This feature somewhat limits the flexibility of the devices since they cannot readily be moved from one location to another, as when the owners of the pet go on vacation.
There are also known in the prior art shelters for small animals, such as those disclosed in U.S. Pat. Nos. 2,932,279 and 3,738,322. Such shelters are typically in the nature of rectangular housings which are constructed for being mounted within a wall opening, such as a window of a basement, with substantially the full length of the housing being projected interiorly of the building structure from the opening or window. Shelters of this type are intended to be used by persons who enjoy having small animals but do not desire to admit the animal to the interior of the house. Accordingly, such shelters prevent the animals to be fully exposed to the elements and generally permits the animal to have the comfort and warmth that results from the animal being indoors. While openings are provided for permitting free movements of the animal between the housing and the outside of the house, the movements between the housing and the interior of the house are generally limited. In the animal shelter of U.S. Pat. No. 3,738,322, the housing is made out of an impervious wall which prevents the transmission of odors from the animal shelter to the interior of the building.